Lead zirconate titanate referred to as PZT is known as a material of a piezoelectric film used for a piezoelectric actuator, for example. PZT is large in piezoelectric constant (i.e. strain per applied voltage) but low in withstand voltage about 10 to 20 V/μm. Thus, insulation breakdown of PZT may occur easily.
Patent Document 1 (JP 2000-326503 A corresponding to U.S. Pat. Nos. 6,502,928 B1, 6,336,717 B1) teaches a piezoelectric element that includes a lower electrode and an upper electrode which are disposed on an insulator layer, and a piezoelectric body layer disposed between these electrodes. A withstand voltage of the piezoelectric body layer is increased by disposing the piezoelectric body layer to cover a lateral surface of the lower electrode.
However, the piezoelectric element of Patent Document 1 may have a part that is deformed due to applied voltage, and a part that is not deformed due to the applied voltage. In a boundary between these areas, a stress may increase and cause cracking. As a result, a leak current may increase, and insulation breakdown of the piezoelectric element may occur.